1. Field of the Disclosure
The present disclosure relates generally to a method of and system for planning a surgery, such as selecting a size and position for an orthopedic prosthesis implant.
2. Background
Computer aided surgical systems for orthopedic and/or arthroplasty procedures are useful for both planning and executing various procedures. One known system and method is described in U.S. patent application Ser. No. 11/290,039, filed Nov. 30, 2005, which is incorporated by reference in its entirety herein. Another known system and method is described in U.S. patent application Ser. No. 10/961,455, filed Oct. 8, 2004, and published as U.S. Patent Application Publication No. 2006/0095047, which is incorporated herein by reference in its entirety.
As diagrammatically shown in FIG. 1, a total knee arthroplasty surgical procedure includes removing affected sections of a distal end of a femur 10, including lateral condyle 12 and medial condyle 14, and an opposing proximal end of a tibia 16 and replacing the removed bone portions with prostheses, including a femoral implant 18 for attachment to a the femur and a tibial implant 20, which includes a base plate 22 for attachment to the tibia and an articular surface 24. To accomplish this, a surgeon resects the condyles at the distal end of the femur to have a shape (shown in dashed lines) complementary to an inner surface 26 of the femoral implant 18 in order to accept the femoral implant thereon. The surgeon also resects the proximal end of the opposing tibia 16 in a shape (shown in phantom dashed lines) to complementarily receive the base plate 22 thereon. The femoral implant 18 and the base plate 22 are secured, such as with adhesive or fasteners, to the respective bones 10 and 16, and the articular surface 24 is secured to the base plate facing the femoral implant. After the patella (not shown for clarity) and soft tissues, including tendons and muscles (not shown for clarity), are properly repositioned around the knee, the femoral implant 18 is able to articulate on the articular surface 24 in a manner resembling natural knee motion.
A navigation system may be used to obtain data during the total knee replacement procedure in order to create a map of relevant portions of the patient, such as the femur 10, femoral condyles 12 and 14, tibia 16 and tibial plateau, fibula, and patella, which may then be displayed on a display, such as a video or computer monitor. One possible mapping system may use, for example, a navigation system as disclosed in Patent Application Publication No. 2001/0034530, in conjunction with a tracking device as disclosed in U.S. Patent Application Publication No. 2005/0199250, published Sep. 15, 2005, each of which is incorporated by reference herein in its entirety. In other possible systems, the mapping data may be obtained by other known pre-operative and/or intra-operative techniques. Using the map, a surgeon is then able to virtually plan the remaining steps of the procedure, including choosing a particular size and/or shape of a replacement prosthesis, and then virtually laying out resections in order to obtain a desired final fit and location of the prosthesis on the remaining bone. This step may be performed using a database of known prosthesis shapes and/or sizes that are then compared to the acquired map data and shown juxtaposed and/or superimposed therewith on the display monitor. After the procedure has been fully planned using the map and prosthesis form factor data, the navigation system may be used to track the physical steps of the operation, such as making the various resections so that the surgeon may advance through the procedure according to the plan. In other methods, the steps for executing the plan of the operation may be performed without the aid of a virtual navigation system using other known layout techniques.
The steps of choosing a particular prosthesis and choosing a preferred layout of the prosthesis on the existing bone have, until now, been dependent wholly or in large part on the skill and experience of the person planning the procedure, such as the surgeon. For example, in a method of visually choosing and adjusting the prosthesis, after obtaining the map of the relevant bones, the surgeon would manually choose a specific size of prosthesis based on his or her experience in visual comparison to the map of the bone. The surgeon—after indicating to the computer which prosthesis was being used—would then visually adjust the position of the prosthesis in comparison with the shape of the appropriate bone (as shown virtually superimposed together on the display screen) by trial and error until a desired position was chosen. The surgeon would then cause the computer to record the chosen position in relation to the map and then use that information to guide the remaining steps of the procedure. Other techniques may simply select a prosthesis size and position based on a single parameter, such as minimizing or eliminating any steps, or notches, in a resected surface of the bone, which may cause localized stress concentration points where premature failure may be more likely to occur.
The method of visually choosing and adjusting the prosthesis can give rise to certain challenges. One challenge—choosing the correct size of prosthesis—is limited by the ability of the surgeon to choose the correct size based solely on the map information of the bones. Another challenge—positioning the prosthesis in the best arrangement with respect to the bone—is limited by both by the size of the prosthesis chosen by the surgeon and the ability of the surgeon to visualize the optimum positional arrangement. A detriment to choosing a non-optimal position and/or size of the prosthesis may be the creation of a notch or an area where the edge of the prosthesis and the surface of the bone do not align well and require an undesirably large runout of the resected portion of the bone beyond an end of the prosthesis or a large overhang or gap between the end of the prosthesis and uncut portions of the bone. A major constraint on the ability of the surgeon to most efficiently plan the procedure is that time is of the essence during a surgical procedure in order to minimize the time during which the patient is incised, and, often, planning can only be initiated and/or completed after the patient has been incised.
Therefore, it would be desirable to have a system and method that will facilitate more accurate and time efficient planning of the procedure to help ensure that an optimal size and position of the prosthesis is planned in order to prevent or minimize the creation of notches in the bone and other inefficiencies and/or less desirable design alternatives.